The disclosure of Japanese Patent Application No. 2002-124952 filed on Apr. 25, 2002, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a vehicle drive control apparatus and, more particularly, to a vehicle drive control executed in a coast state of the vehicle where a throttle valve is fully closed.
2. Description of Related Art
There is a known vehicle drive control apparatus including (a) an engine that generates power through combustion of fuel, (b) a fluid power transmission device having a lock-up clutch for transmitting the power through fluid, (c) a unit for executing a fuel cut control that stops supply of the fuel upon establishment of a fuel cut condition including that a vehicle is in a coast state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than an engine speed at release of the fuel cut operation (hereinafter referred to as F/C release engine speed), and (d) a unit for engaging the lock-up clutch upon establishment of a lock-up clutch engagement condition including that the vehicle is in the coast state. For example, in an apparatus disclosed in JP-A-9-53718, the lock-up clutch is slip engaged in the coast state such that the engine speed is increased and the fuel cut range (vehicle speed range) is expanded, thus improving the fuel efficiency.
In the above-described vehicle drive control apparatus, a reverse input of the driving wheels causes the engine speed to be increased, generating the engine braking force. Upon downshifting in the automatic transmission as decrease in the vehicle speed, an inertia caused by the change in the engine speed considerably varies the engine braking force, which may cause the occupant of the vehicle to feel a certain shock. If the vehicle speed in the coast state at downshifting is reduced as low as possible, the range of the change in the engine speed can be decreased, thus reducing the shock. In the aforementioned case, however, the engine speed may become lower than the F/C release engine speed at rapid deceleration of the vehicle such that the fuel supply is resumed, thus deteriorating the fuel efficiency. As the coast down vehicle speed is set to be relatively higher in order to continue the fuel cut operation (interruption of the fuel supply), the shock resulting from shifting is likely to occur. Reducing the shock by decreasing the shifting speed, however, may lower the engine speed below the F/C release engine speed during shifting.
In the case where the lock-up clutch is not slip controlled for a certain reason (for example, the temperature of the work fluid is low), the engine speed is decreased and thus the fuel cut is not operated. When downshifting is performed at the same speed as that of the aforementioned state, the rotational speed of the input shaft considerably changes to cause the shock owing to the change in the engine speed even if the lock-up clutch is in an OFF state.
In the case where the idling speed of the engine is increased to be higher upon actuation of an accessory such as an air conditioning unit, assuming that the F/C release engine speed is set to a constant value, the engine speed changes at release of the fuel cut operation, resulting in the shock. If the F/C release engine speed is increased to cope with the change in the idling speed, the engine speed may become lower than the F/C release engine speed such that the fuel supply is resumed, deteriorating the fuel efficiency.
Generally the slip control of the lock-up clutch is executed through a feedback control such that the slip amount of the lock-up clutch approaches a predetermined target slip amount. The feedback control is stopped at downshifting operation where the engine speed changes sharply because of low response. The slip control is executed through a feed-forward control (at a constant engagement torque) only. If the engagement torque of the lock-up clutch is set to a lower value, the engine speed is decreased to be lower than the F/C release engine speed. As a result, the fuel supply is resumed, deteriorating the fuel efficiency. On the contrary, if the engagement torque is set to a higher value, the engine braking force changes sharply, the shock is likely to occur. If the feedback control is resumed after completion of shifting in the state there the deviation between the actual and the target slip amounts is large, the slip amount, that is, the engine speed may be changed in accordance with the deviation. The sharp change in the engine braking force, thus, may cause the vehicle occupant to feel the shock.
It is an object of the invention to provide a technology that prevents generation of a shock owing to the sharp change in the engine braking force at downshifting, or deterioration in the fuel efficiency owing to resumption of the fuel supply caused by the engine speed lower than the F/C release engine speed in a coast state where the fuel cut control and the lock-up clutch engagement control are executed.
According to an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, a fluid power transmission device interposed between the automatic transmission and the engine for transmitting power through fluid, the fluid power transmission device having a lock-up clutch, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a control for engaging the lock-up clutch upon establishment of a lock-up clutch engagement condition including that the vehicle is in the coasting state, and executes a control of the automatic transmission for downshifting at a coast down vehicle speed that changes in accordance with a state of the lock-up clutch under the control for engaging the lock-up clutch.
In the aforementioned embodiment, the controller sets the coast down vehicle speed at which the lock-up clutch is engaged to be higher than the coast down vehicle speed at which the lock-up clutch is disengaged.
In the vehicle drive control apparatus, the downshifting is performed by the automatic transmission at a coast down vehicle speed that is set depending on the engagement state of the lock-up clutch. If the coast down vehicle speed at which the lock-up clutch is engaged is set to the value higher than the coast down vehicle speed at which the lock-up clutch is disengaged, downshifting can be performed while continuing the fuel cut operation in the state where the lock-up clutch is engaged. This makes it possible to improve the fuel efficiency. Meanwhile, if there is a high possibility that the fuel cut operation is not executed because of decrease in the engine speed when the lock-up clutch is disengaged, the downshifting is performed at a low vehicle speed. Therefore, the change in the rotational speed of the related portions along with the downshifting performance may be reduced, thus preventing the downshifting shock.
In the embodiment, the controller sets the coast down vehicle speed at which the lock-up clutch is disengaged is higher than the coast down vehicle speed at which the lock-up clutch is engaged.
If the coast down vehicle speed at which the lock-up clutch is disengaged is set to the value higher than the coast down vehicle speed at which the lock-up clutch is engaged, downshifting can be performed while continuing the fuel cut operation in the state where the lock-up clutch is engaged. Even in the state where the lock-up clutch is disengaged, if the coast down vehicle speed is set to be relatively higher such that the engine is caused to be operated accompanied with the fluid power transmission device to continue the fuel cut operation, downshifting can be performed while continuing the fuel cut operation, thus further improving the fuel efficiency.
According to an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined fuel cut release engine speed, and changes a coast down vehicle speed and upshifting vehicle speed in accordance with a change in the fuel cut release engine speed so as to continue the fuel cut control irrespective of the change in the fuel cut release engine speed.
In the case where the idling speed is changed in accordance with ON/OFF operation of accessories, for example, an air conditioning device such that the F/C release engine speed is changed, the coast down vehicle speed and the upshifting vehicle speed are changed in accordance with the change in the F/C release engine speed such that the fuel cut operation is continued irrespective of the change in the F/C release engine speed. The fuel cut operation, thus, can be continued as well as improve the fuel efficiency. As the coast down vehicle speed is changed in accordance with the change in the F/C release engine speed, it can be set to be as low as possible. The resultant change in the engine speed accompanied with the downshifting and further the change in the engine braking force may be decreased to reduce the resultant shock.
According to an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a control of the automatic transmission for downshifting at a predetermined coast down vehicle speed so as to continue the fuel cut control in the coasting state, and executes a control of changing a downshifting speed such that the downshifting speed increases as an increase in a deceleration of the vehicle.
In the embodiment, the downshifting speed is increased as the increase in the deceleration of the vehicle. If the deceleration is relatively high, the downshifting operation can be smoothly performed. As a result, the time period from the time at which the engine speed reaches the F/C release engine speed to the time at which the fuel supply is released may be elongated so as to improve the fuel efficiency. If the deceleration is relatively low, the downshifting speed is at a relatively lower. As a result, each change in the engine speed or the engine braking, may be gentle, thus preventing generation of the resultant shift shock.
When the deceleration is relatively higher, it is normally determined that the braking operation is performed. Therefore, there is a low possibility of causing the vehicle occupant to feel the shift shock even if the shifting speed increase. If the coast down vehicle speed is made higher in case of the large deceleration of the vehicle, the time period taken until resumption of the fuel supply may be elongated by lowering the engine speed at downshifting. This may reduce the hysteresis relative to the upshifting, which has a possibility of causing the vehicle operator to feel frequent shifting at operation of the accelerator pedal, which may be disadvantageous
According to an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, a fluid power transmission device interposed between the automatic transmission and the engine for transmitting power through fluid, the fluid power transmission device having a lock-up clutch, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a control for engaging the lock-up clutch upon establishment of a lock-up clutch engagement condition including that the vehicle is in the coasting state, executes a control of the automatic transmission for downshifting at a predetermined coast down vehicle speed so as to continue the fuel cut control in the coasting state, and executes a feedback control of an engagement torque of the lock-up clutch such that a slip amount of the lock-up clutch reaches a target slip amount upon execution of the control of the automatic transmission for downshifting.
In the embodiment, the engagement torque of the lock-up clutch is feedback controlled such that the slip amount of the lock-up clutch reaches a target slip amount at downshifting. As the slip amount can be controlled so as not to be excessive, the engine speed does not decrease to be lower than the F/C release engine speed. Accordingly, the fuel supply is not resumed, preventing deterioration in the fuel efficiency. This makes it possible to prevent a large decrease in the engine speed owing to the excessive slip amount. Therefore the coast down vehicle speed can be set to the value as low as possible so as to reduce the shock resulting from shifting by decreasing the change in the engine speed and further the change in the engine braking force.
In the embodiment, the controller continues the feedback control of the engagement torque of the lock-up clutch at least until a timing when a rotational speed of an input shaft of the automatic transmission starts changing upon the downshifting and stops thereafter.
According to the embodiment, the deviation between the actual and the target slip amounts does not expand until the timing when the rotational speed of the input shaft of the automatic transmission starts changing at downshifting, that is, the start of the inertia phase. This makes it possible to execute the feedback control until when the deviation between the actual and the target slip amounts is expanded by the change in the rotational speed of the input shaft, and to stop the feedback control so as to restrain the decrease in such rotational speed of the input shaft. This may restrain the shock resulting from shifting owing to sharp change in the engine speed, and further the engine braking force.
In an embodiment, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, a fluid power transmission device interposed between the automatic transmission and the engine for transmitting power through fluid, the fluid power transmission device having a lock-up clutch, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a feedback control of an engagement torque of the lock-up clutch such that a slip amount of the lock-up clutch reaches a target slip amount upon establishment of a lock-up engagement condition including that the vehicle is in the coasting state, and executes a control of the automatic transmission for downshifting at a predetermined coast down vehicle speed so as to continue the fuel cut control in the coasting state. The feedback control of the engagement torque of the lock-up clutch is temporarily stopped upon downshifting, and a performance ability of the feedback control of the slip amount is temporarily lowered upon resumption of the feedback control of the engagement torque of the lock-up clutch after the downshifting.
According to the embodiment, the feedback control is temporarily stopped upon downshifting. This makes it possible to prevent expansion of the deviation between the actual and the target slip amounts accompanied with the change in the rotational speed of the input shaft of the automatic transmission in the downshifting. Therefore, this may restrain the shift shock owing to sharp change in the engine speed, and further the engine braking force. Upon resumption of the feedback control after the downshifting, the performance ability of the feedback control of the slip amount is temporarily lowered. As a result, sharp change in the engine speed and further the engine braking force caused by the deviation in the slip amount may be avoided at resumption of the feedback control, thus restraining the shift shock.
In the embodiment, the controller temporarily increases the target slip amount to a temporal target slip amount in accordance with an actual slip amount upon resumption of the feedback control after the downshifting, and gradually returns the temporal target slip amount to the target slip amount that has been previously set.
According to the embodiment, the target slip amount is temporarily increased in accordance with the actual slip amount, and then, the increased target slip amount is gradually returned to the previously set target value upon resumption of the feedback control in the downshifting. This makes it possible to return the slip amount that has been increased as the change in the rotational speed of the input shaft upon downshifting to the previously set target slip amount. As the engine speed and the engine braking force are gradually changed accordingly, the shift shock may further be restrained.
In an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a control of the automatic transmission for downshifting at a predetermined coast down vehicle speed so as to continue the fuel cut control in the coasting state, and temporarily expands an air passage. in an intake side of the engine while continuing execution of the fuel cut control during the downshifting.
According to the embodiment, the air passage of the intake side of the engine is temporarily expanded while continuing the fuel cut operation in the downshifting. The engine braking force is decreased by the pumping, effect, and the shift shock may be restrained by preventing sharp increase in the engine braking force caused by the change in the engine speed in the downshifting.